Rescue devices have been used by persons who are active in areas subject to avalanches. These devices typically may be employed either in a transmit mode or a receive mode. The device is normally carried or worn by the user while active in the transmit mode, where the device transmits a modulated electromagnetic signal at a specified frequency. If the user is buried by an avalanche, a rescuer using a similar device in the receive mode can detect the transmitted signal and use the signal to locate the buried person.
Such avalanche rescue devices typically have a variety of common elements. They have a transmitter which generates a pulsed electromagnetic signal at a specified frequency. An antenna is provided which serves to transmit the pulsed electromagnetic signals when they are being generated.
These avalanche rescue devices also have a receiver which, in combination with the antenna, is designed to receive signals being transmitted by another rescue device operating in the transmit mode. The transmitter, antenna, receiver, and a battery pack which serves as a power source, are packaged in a case and provide a compact unit which can be readily worn or carried. When worn, a harness constructed from one or more belts is provided for securing the case to a person. The harness in turn attaches to the case with a first belt connector and a second belt connector.
For safety reasons, it is desirable to design the rescue device such that it is difficult for the user to inadvertently carry the device with the power off or in the receive mode. If the device is not active in the transmit mode when the user is buried by an avalanche, rescuers may be unable to locate the user. One prior art rescue device which offers a high degree of safety is the F1 Focus avalanche transceiver device designed by the present inventor. The F1 Focus offers several features which reduce the likelihood of the device being worn or carried while not active in the transmit mode.
The F1 Focus device has an antenna, a transmitter/receiver circuit, and a battery which are housed in a case. The case is designed to be worn by the user, and when in use is attached to the user by a harness made up of belts. The belts connect to the case via a first belt connector and a second belt connector. The first belt connector is detachable from the case, while the second belt connector is permanently attached to the case.
The first belt connector has a T-shaped protrusion which is designed to fit into a receptor slot on the case. To connect the first belt connector to the case, the T-shaped protrusion is placed into the receptor slot and rotated to lock the T-shaped protrusion therein and secure the device to the user.
To assure that the device is active when secured to the user, the first belt connector is configured to operate a power switch which activates and deactivates the device. Insertion of the T-shaped protrusion into the receptor slot moves the power switch to a position where it completes a circuit between the battery and the transmitter/receiver circuit to activate the device. Turning and removing the T-shaped protrusion from the receptor slot allows the power switch to return to a position where the circuit is broken, and the device is inactive. While the interaction of the first belt connector and the power switch provides increased safety for the user, the requirement that the belts be attached to the case in use may be inconvenient when the user desires to carry the device in a pocket or pouch.
The device has a transmission status light on one side of the case. The transmission status light is positioned such that the user may wear the device with the transmission status light readily visible. The transmission status light is illuminated when the device is active in the transmit mode, providing notice of such to the user.
The device also has a combination mode/sensitivity switch which allows the user to manually switch the device between its transmit and receive modes, and, when the device is in the receive mode, allows the user to adjust the sensitivity of the receiver. The mode/sensitivity switch is a rotary switch having a transmit position, where the transmitter is active, and a number of receive positions in which the receiver is active. The different receive positions correspond to decreasing levels of sensitivity of the receiver when detecting a transmitted signal.
The mode/sensitivity switch also has a transmit lock device. When the mode/sensitivity switch is in the transmit position, the transmit lock device prevents the user from turning the mode/sensitivity switch unless the transmit lock device is first manually retracted. The transmit lock device thus helps prevent the user from inadvertently turning the device from the transmit mode to the receive mode. The mode/sensitivity switch may be freely turned from any of the receive positions to the transmit position.
When being used in the receive mode to locate a buried person, the user initially turns the mode/sensitivity switch to the highest sensitivity position. In this position, the response of the receiver to a transmitted signal received via the antenna is greatest. If no signal is detected, the user is trained to execute a broad search pattern until a signal is found. When a signal is detected, a speaker provides an audio output, the volume of which is proportional to the response of the receiver. As the searcher approaches the buried person along a field line of the transmitted signal, the strength of the signal received increases, and the response of the receiver correspondingly increases.
While most avalanche rescue devices provide an audio output, the F1 Focus additionally features three signal strength indicator lights. These signal strength indicator lights are progressively illuminated as the response of the receiver increases. When the response of the receiver is sufficiently great that the audio output of the speaker is very loud and all three signal strength indicator lights are illuminated, the user turns the mode/sensitivity switch to the next receive position, where the response of the receiver to a given signal strength is reduced. This procedure is repeated until the least sensitive receive position of the mode/sensitivity switch is used. In this position, when the response of the receiver is sufficiently great that the audio output of the speaker is very loud and all three signal strength indicator lights are illuminated, the user is trained to execute a pinpoint search to determine the location of the buried person with a high degree of precision, and then digs down to uncover the buried person.
While the volume of the audio output and the three signal strength indicator lights provide the user an indication of the strength of the signal being received, this may or may not correspond to the distance to the buried person. If the signal is to continuously increase, the searcher must follow a curved field line to reach the buried person, rather than taking a straight path. Increased precision in the indication of signal strength helps provide notice to the user when they have moved off of the field line they are following and thus helps the user to effectively reach the buried person.
In an attempt to provide the user increased precision in indicating an estimated distance to the buried person, a device having a pair of antennas has been employed. However, this device requires complicated circuitry to estimate the distance from the relative signal strengths received from each antenna, rather than simply measuring signal strength along a field line with a single antenna. The device then presents the distance on a digital display. Such dual antenna devices have been found to be sensitive to orientation, and may provide signal strength differences of 5:1 for differing orientations at the same distance.
A concern with all such rescue devices is the training required for their effective use. Speed in locating and uncovering the buried person is of primary importance in rescue situations, and any hesitation on the part of the rescuer may reduce the chance of survival of the buried person. Additionally, witnessing an avalanche is traumatic, and may impair the ability of the searcher to remember what appropriate actions to take. An additional concern when multiple searchers are employed is the possibility that one or more of the searchers may inadvertently have their rescue device in the transmit mode. This may interfere with the other searchers receiving signals from the buried person.
Thus, there is a need for a rescue device which does not require the belts to be attached for use, which provides increased precision in indicating signal strength to the user, and which is readily operated with minimal training and/or under traumatic conditions.